This invention generally relates to the field of sporting goods including golf clubs and in particular golf club heads. The invention relates to using plasma immersion ion implantation (PIII) and/or plasma immersion ion deposition processes to produce a hard, diamond-like coating on an article to increase the surface hardness, durability, and corrosion resistance of the article.
The market for sporting goods in the U.S. (and the world) has grown significantly over the past ten years. For example, over 20 million Americans play recreational golf each year, and increasing numbers of these golfers are willing to pay large sums of money for golf equipment utilizing new technologies that offer performance advantages. Consequently, designers of sporting equipment such as golf clubs continually seek to optimize their design and construction, including innovative selection of club head and shaft materials, to achieve maximum performance. Along with improvements that increase the distance that a ball will be propelled after being struck, two other leading issues that golf club designers have attempted to address include durability and directional accuracy.
Traditional clubs having heads made of hard wood (which tend to warp or split and are often costly) have given way to the development of heads made of engineered materials, such as steels, cast irons, aluminum, copper, titanium, graphite, plastics, carbides, and the like. In addition, because Young""s Modulus (which expresses the rigidity of a material) teaches that the greater the rigidity of a material, the greater will be the distance traveled by the ball, some designers have coated these engineered materials with other materials in an attempt to increase the hardness of the striking surface. However, as discussed in U.S. Pat. No. 5,851,158 to Winrow et al. (which is incorporated herein by this reference), many of these coating methods have poor bond strength and chip during normal use of the golf clubs. Moreover, current methods of applying these coatings result in coatings that are too thin to provide sufficient wear resistance.
Some designers have suggested using diamond, the material with the highest known Young""s Modulus, as a coating material for golf clubs. For example, U.S. Pat. No. 4,951,953 to Kim, (hereinafter xe2x80x9cKimxe2x80x9d) which is incorporated herein by reference, describes applying a coating about 0.5 mil to 5 mil thick containing at least 10% of a material having a Young""s Modulus of 50 million pounds per square inch (psi) to golf club heads. Kim indicates that diamond, which has Young""s Modulus of 130-170 million psi, is the preferred material. However, Kim states that economic and technical limitations (then in existence) prevent applying a coating of pure diamond on a golf club. Instead, Kim teaches coating golf clubs with an electroless composite material where diamond particles are embedded in a metal or metal alloy matrix such that the diamond particles are weakly cemented together by the soft metal without any diamond-diamond bonds.
Other golf club designers have recognized the desirability of using pure diamond at the striking surface of a golf club, but have not coated the entire golf club or golf club head with diamond. For example, U.S. Pat. No. 5,620,382 to Cho et al. (which is incorporated herein by reference) teaches providing a golf club with a ball striking face that has an insert made of a material, such as polycrystalline diamond (PCD), where the individual crystals are bonded together by diamond-diamond bonds. The insert typically is located in the xe2x80x9csweet spotxe2x80x9d of the club face, thus the remainder of the club face does not necessarily benefit from the scratch and chip resistant diamond insert. Moreover, the diamond insert substantially increases the expense and complexity of manufacturing the golf club.
In recent years, new processes have been developed that can selectively alter the structure and physiochemical properties of the surfaces of materials such as metals, plastics, glass, and ceramics. Such advanced processes for metal treatment and hardening represent a multi-billion dollar business in the U.S. One of the most promising of these processes is plasma immersion ion implantation (PIII) (also referred to as Plasma Source Ion Implantation (PSII)), described herein, in which metal surfaces can be conformally implanted with a flux of high energy ions with minimal distortion or surface heating. Another such process described herein is called plasma immersion ion deposition, in which a thin, hard coat of a substance is applied to an irregular surface. However, the industrial application to date of PIII and plasma immersion ion deposition has been limited to laboratory environments and to a few experimental large-scale processes. Practical commercial implementations of these technologies are hindered by the lack of automated, commercially usable manufacturing processes and systems capable of simultaneously providing high voltage pulsed power, vacuum pumping, and plasma generation. To date, no art appears to teach coating golf club heads using plasma immersion processes.
Accordingly, it is one objective of the present invention to provide a commercial scale PIII system capable of performing the PIII process and/or the plasma immersion ion deposition process in an automated fashion.
It is further an objective of the present invention to provide a system and method for treating a workpiece, which can comprise one or more articles to be hardened, with the PIII process where the system comprises a chamber under a vacuum, in which the workpiece is placed; a plasma generator for generating plasma from a gas fed into the chamber such that the plasma immerses the workpiece; and a high voltage pulser for pulsing the workpiece at high negative voltages, thereby accelerating the ions in the plasma normal to the surface of the workpiece, whereby the entire surface of the workpiece is implanted with a flux of energetic plasma ions without mechanical manipulation, as would be required for conventional beam-line implantation.
It is yet another object of the invention to optimize the system and method for performing the PIII process. In one embodiment, the plasma generating mechanism generates plasma using any of a number of known plasma generation methods, such as RF powered inductive coupling that is pulsed in timed synchronization with the high voltage pulses that are generated at the high voltage pulser, to minimize the average power required by the system. In another embodiment, the vacuum for the chamber is provided by a vacuum pump system comprising diffusion pumps, a cryogenic cold trap to prevent back streaming of the oil in the diffusion pumps, and a pump control system that optimizes the gas throughput and pump speed to reduce the cycle time needed to perform the PIII process.
It is another objective of the present invention to provide a workpiece having improved durability, scratch resistance and accuracy. In one embodiment, the workpiece comprises one or more golf clubs each comprising a head and a shaft, wherein at least a portion of the golf club is treated with the PIII process to produce a hardened golf club. The material used to treat the surface of the one or more golf clubs preferably has a high Young""s Modulus and a relatively low weight density to minimize the weight added to the one or more golf clubs. In one embodiment, diamond or a diamond-like-carbon (DLC) is used to treat the one or more golf clubs. In another embodiment, only a portion of the head of the one or more golf clubs is treated with the PIII process. In yet another embodiment, the entire golf club head is treated with the PIII process.
This invention results from three interrelated realizations: (1) That line of site ion implantation methods can not be used to coat relatively inexpensive and irregularly shaped non-industrial articles such as golf club heads because of the special fixturing required; 2) that coating such articles using time consuming ion immersion techniques is only cost effective if a large number of articles are coated at once; and 3) that the current level applied to the articles must be tailored depending on the number articles to properly coat each article.
Thus, in this invention, the number of articles coated at once is a function of the cost of each article and the peak current level or power level used to coat the articles is a function of the number of articles. In this way, hundreds and even thousands of golf club heads or other sporting good articles can be coated by the plasma vapor deposition, plasma immersion implantation, or plasma immersion ion processing methods without adversely increasing the cost of the golf club heads and yet at the same time resulting in extremely durable and scratch resistant golf club heads.
Other objects and advantages of the present invention will become apparent from the following detailed description when viewed in conjunction with the accompanying drawings, which set forth certain embodiments of the invention.